1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus, and more specifically, for example, relates to a method of writing a pattern on a target object on the stage by radiating multiple beams (multibeams).
2. Description of Related Art
The lithography technique that advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high in Legration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with an electron beam.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multibeams) can be cited. Compared with the case of writing a pattern by using an electron beam, since it is possible to emit multiple beams at a time in multiple writing, the throughput can be greatly increased. In the writing apparatus employing a multibeam system, for example, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes, blanking control is performed for each of the beams, and each unblocked beam irradiates a desired position on a target object or “sample” (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2006-261342).
In an electron beam writing apparatus, each beam shot is focused on a target object surface by an objective lens, and then focus correction (dynamic focusing) is dynamically performed during writing in order to deal with convex and concave of the target object surface by using an electrostatic lens, for example. However, when dynamic focusing is performed, a rotation change occurs in a beam image on the target object surface, and moreover, a magnification change also occurs. Such problems degrade the accuracy of writing position. In the case of a single beam system, since the number of beams is one, a rotation change and a magnification change will occur with respect to one shot, thereby producing a positional error that is not so large in many cases. However, in the case of a multibeam system, as being different from the single beam system, since the number of beams of one shot which are simultaneously irradiating is a large number, if a rotation change and a magnification change occur in the entire multiple beams, a writing positional error may be an unallowable one. Therefore, it is required to reduce as much as possible the rotation change and magnification change of an image due to dynamic focusing. However, when performing such correction using many optical instruments, there occurs a problem that the installation space in the electron lens barrel becomes insufficient.